1. Field of the Invention
The present invention relates to a degradation determining apparatus for a power storage device and a degradation determining method for a power storage device, and more particularly to a technique of determining a degradation state of a power storage device mounted on a vehicle for driving.
2. Description of the Background Art
Japanese Patent Laying-Open No. 9-7642 discloses a charger having a function of diagnosing and determining abnormality and performance degradation of a secondary battery. This charger has three operation modes, namely, a charging mode, a refresh mode, and a diagnosis mode. In this charger, when a secondary battery is new or as good as new, charging and discharging is once performed in the diagnosis mode, and the charging capacity, the discharging capacity, and the terminal voltage at the time of completion of charging are stored in a storage unit. Then, after the secondary battery is used multiple times, the charging capacity, the discharging capacity, and the terminal voltage at the time of completion of charging are measured again in the diagnosis mode and compared with the data for the new battery stored in the storage unit in order to determine the degree of degradation.
In the charger disclosed in Japanese Patent Laying-Open No. 9-7642, however, a degradation state of a secondary battery is determined by measuring a state for a new secondary battery to be diagnosed for storage into the storage unit and measuring a state again for comparison with that of the new one after the secondary battery is used multiple times. Therefore, the degradation state can be determined only with the particular charger having the data for the new battery stored therein.
In the above-noted charger, the degradation state of the power storage device is determined using the secondary battery characteristic data that is measured during charging or diagnosis. However, sufficient degradation determination accuracy may not be obtained only with such measurement data.